The present invention relates to packet/cell switching networks or ATM networks, and more particularly to a method and system for dynamically adjusting the bandwidth of a Continuous Bit Rate Virtual Path Connection (CBR VPC) according to the current network resource reservation.
HIGH SPEED COMMUNICATION NETWORKS
In nowadays telecommunication networks, different types of applications must share the same transmission media, and networks equipment must be able to support these different services while guaranteeing to each of them a specified quality of service. While some years ago, voice and data were using separate networks, they now share bandwidth of the same links. For the last three years, standard organisms have worked to define transmission modes, such as ATM (Asynchronous Transmission Mode), Frame Relay, . . . and inside a particular transmission mode, to specify in detail the services provided to network applications. For ATM, for instance, four different service categories exist, and a user will choose one of them based on the type of service required:
Continuous Bit Rate (CBR)
This service is intended for uncompressed voice, and highest priority applications (video). The price to pay for this service is the highest because the bandwidth which is reserved, corresponds to the maximum rate (Peak Cell Rate PCR) at which this type of applications can emit. This is the bandwidth to allocate when the quality of service, in terms of maximum Cell Transfer Delay (maxCTD) and Peak to peak Cell Delay Variation (peak to peak CDV), must be guaranteed whatever the network load conditions.
Variable Bit Rate (VBR)
This service is a compromise between the Continuous Bit Rate (CBR), which requires a lot of resources, and a service where no reservation of bandwidth would be done. Effectively here, a bandwidth comprised between the Sustainable Cell Rate (SCR) of the connection and the Peak Cell Rate (PCR) of said connection is allocated, depending on the burstiness of the traffic:
When the bursts created by the application in the network are limited, a bandwidth close to the Sustainable Cell Rate (SCR) is reserved.
When the bursts induced by the application are large (or may be large), a bandwidth closer to the Peak Cell Rate is reserved to avoid links and buffers overload, and data discard.
While the service offered here also guarantees a very low loss of packets or cells (Cell Loss Ratio CLR), the transfer delays and cell delay variations are more important than for CBR. VBR can be divided in VBR Real Time (good candidate for video and data RT applications) and VRB Non Real Time (good candidate for data sensitive traffic).
Unspecified Bit Rate (UBR)
This service is totally uncontrolled. Traffic is sent in the network, and is transmitted provided that the network is not congested. When the network is congested, cells are discarded. Unlike CBR and VBR, no quality of service can be guaranted.
Available Bit Rate (ABR)
This service provides again less quality than Variable Bit Rate (VBR), and can be used for different applications. While a minimum reservation can be done in the network to guarantee to an application a xe2x80x9cworst casexe2x80x9d behaviour, the steady state behaviour of the service offered corresponds to a xe2x80x9cnon reservedxe2x80x9d type of service, where nearly no resource is allocated in the network. When congestion occurs, feedbacks are conveyed through the network back to the traffic sources to prevent them from sending more data. This reactive system behaviour is directly linked to the network size. The delay to convey back congestion information to the sources increases in function of the network size, and may induce losses anyway. In this case, end users take decisions to send again the data. Here nor the delays neither the losses can be guaranteed; the service is only assumed to minimise the losses.
All these different services are proposed and used simultaneously in most networks.
BANDWIDTH OPTIMISATION
Most of the wide ATM networks (large country, world-wide networks) are configured so that an ATM backbone network can support the communications between different ATM access networks. Such network topology allows good performances and the optimisation of the network administration. Generally, the backbone network is a public ATM network, and access networks are private ATM networks. However, the backbone can be used within a single private network using for example lines leased from a carrier. To optimise the resources where they are the more demanded, in particular the bandwidth within the backbone network, several solutions can be implemented, all taking into account the dynamic availability of the bandwidth:
1. End to end Available Bit Rate Virtual Channel Connections (ABR VCCs) for data traffic.
This solution, as illustrated in FIG. 5, supposes the support the ABR service by all end-systems (nodes 1 and 8). The advantage is that intermediate nodes (nodes 2 to 7) have only to set an Explicit Forward Congestion Indication (EFCI) bit in the ATM cells to be compliant with the ATM Forum recommendation (ATM Forumxe2x80x94Technical Committeexe2x80x94xe2x80x9cTraffic Management Specificationxe2x80x9d, version 4.0, April 96, paragraph 5.10.6, rule 1.a)). End-systems (nodes 1 and 8) do the most complex process in particular:
the ABR source behaviour (node 1) including:
generation of Resource Management cells (RM-cells),
insertion of RM-cells in the traffic,
computation of a transmission rate per VCC based on congestion information received from RM-cells,
dynamic traffic shaping,
and, the ABR destination (node 8) behaviour including:
transmission of RM-cells back to the source in response to forward RM-cells,
setting of the congestion fields within RM-cells,
insertion of RM-cells in the traffic, . . .
A more sophisticated implementation of the Available Bit Rate (ABR) category of service in intermediate nodes is described in the ATM Forum paragraph 5.10.6, rule 1.c). The so called xe2x80x9cswitch behaviourxe2x80x9d allows the control of congestion at queuing points and in particular the modification of the Explicit Rate (ER) field within RM-cells for a better response to congestion and thus a lower cell loss.
2. Available Bit Rate Virtual Path Connections (ABR VPCs) in the backbone.
ABR Virtual Path Connections (VPCs), as illustrated in FIG. 6, are set up in the backbone network for interconnecting access networks (access networks 1 and 2). The nodes within the access networks directly connected to the backbone network (nodes 2 and 5) use these ABR VPCs to transport VCCs (VCC1, VCC3). In order to comply with the ATM Forum recommendations (paragraph 5.10.9), these nodes implement the ABR source and destination behaviour as described in paragraphs 5.10.4 to 5.10.9. Access nodes (nodes 2 and 5) must also be able to provide a fair share of the bandwidth of these Virtual Path Connections (VPCs) among the different Virtual Channel Connections (VCC1, VCC3) they support.
The establishment of ABR Virtual Paths Connections (VPCS) allows the aggregation of multiple VCCs and thus a better management of the bandwidth within the backbone network:
VCC Aggregation:
While, most Virtual Channel Connections (VCCs) within access networks don""t require a large amount of bandwidth, the traffic between the different access networks through the backbone network requires as for it, the definition of a large bandwidth connections. The use of Virtual Path Connections (VPCs) considerably limit the number of VCCs which must be established on the backbone network, while optimizing the bandwidth utilization. The response time is generally reduced, avoiding delays in the different policing processes. While in access networks CBR, VBR or ABR/UBR Virtual Channel Connections (VCCs) are established, the backbone network requires usually ABR or CBR VPCs. These Virtual Path Connections must be able to transport any category of service without distinction of quality, through the backbone network.
Bandwidth Management:
The quality of the process used at the backbone/access networks edges to allocate the bandwidth of a VPC among different individual VCC connections determines the overall performance of the end to end service: short delays for high priority traffic (voice or CBR traffic), and smoothing of low priority traffic (data or ABR traffic) even if, within the backbone network, in a same Virtual Path Connection (VPC), all types of traffic are mixed. The different functions of the process for controlling the traffic are:
Smoothing: a shaping function is used to send the traffic of the Virtual Channel Connections (VCCs) on the Virtual Path Connection (VPC), controlling the maximum transmission rate. Delays between consecutive cells are introduced to space the flow.
Queuing: the shaping function lets the traffic leave the node at a lower rate than available. This induces additional queuing in the node. A good implementation allows the storing of data without loss.
Bandwidth Allocation: within a given Virtual Path Connection (VPC), the bandwidth is allocated among the different VCC connections. Rules must be chosen to fairly allocate the bandwidth of a Virtual Path Connection (VPC) taking into account the category of service of the different VCCs (CBR, VBR, ABR, UBR . . . ).
While the Available Bit Rate (ABR) service category is defined in the ATM Forum specifications and provides an efficient bandwidth utilization, its implementation requires important resources in term of:
processing capacity for managing RM-cells along the ABR VPC and continuously (in a time period in the order of the micro or milli second) adjusting the bandwidth.
additional bandwidth. Per default, 1 RM-cell is generated every 32 cells, which represents about 3% additional bandwidth only used for the RM-cell traffic.
Solutions based on equivalent principles (dynamic bandwidth adjustment function of the network availability), but characterized by a slower reaction time (Minutes or seconds instead of microseconds) are then preferred to ABR service category to save resources
The object of the present invention is, in a packet or cell switching network, to dynamically adjust the bandwidth of a Continuous Bit Rate (CBR) Virtual Path Connection (VPC) according to the current network resource reservation and more particularly, in a backbone ATM network where voice calls have priority, to dynamically allocate the remaining bandwidth to data traffic by means of a bandwidth adjustable CBR VPC. The purpose is to guarantee that a number of voice calls, or more generally Switched Virtual Connections (SVCs) can be accepted while allowing the bandwidth to be used by data traffic or Permanent Virtual Connections (PVCs) when these voice calls are not requested.
The present invention relates to a system and method for dynamically adjusting the bandwidth of a continuous bit rate virtual path connection established between a source node and a destination node within a packet or cell switching network comprising a plurality of nodes interconnected with transmission links. In the network, a bandwidth management server having access to information concerning network nodes and transmission links is defined. This server is informed each time a virtual path connection or a virtual channel connection is established on the network with an indication concerning the initial bandwidth reserved for said connection. The server detects and shares on a continuous or periodical mode, the bandwidth which is available on transmission links among the bandwidth adjustable continuous bit rate virtual path connections and determines for each connection a new bandwidth. The source node is informed each time a new bandwidth is computed and it adjusts the bandwidth of the corresponding bandwidth adjustable continuous bit rate virtual path connection accordingly.